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1. Field of the Invention
This invention relates to surgical modifications to the eye. In a specific embodiment, the invention provides ophthalmic surgery techniques which employ a laser to effect ablative photodecomposition of corneal tissue to correct presbyopia and/or other vision defects.
With aging, a condition of the eye known as presbyopia develops. With this condition, the crystalline lens of the eye loses the ability to focus on near objects when the eye is corrected for far-vision.
Presbyopia is often treated with bifocal eyeglasses. With bifocals, one portion of the lens is corrected for far-vision, and another portion of the lens is corrected for near-vision. By looking down through the bifocals, the user looks through the portion of the lens corrected for near-vision. When viewing distant objects, the user looks higher, through the portion of the bifocals corrected for far-vision.
Efforts have been made to treat presbyopia using partitioned lenses positioned directly over the pupil of the eye. Examples include multifocal contact lenses. Unfortunately, when presbyopia is corrected with bifocal or multifocal lenses attached to the cornea, the user is simultaneously looking through the near- and far-vision corrected lenses. As a result, the user will see both in-focus and out-of-focus images simultaneously when viewing an object. This out-of-focus image superimposed on the in-focus image can cause glare and degrade vision when viewing objects at low contrast.
Another technique for treating presbyopia has been to correct one eye of the patient for near-vision and to correct the other eye for distance-vision. This technique is known as monovision. With monovision, a patient uses one eye to see distant objects and the other eye to see close objects. Unfortunately with monovision, the patient may not clearly see objects that are intermediately positioned because the object is out-of-focus for both eyes. Also, a patient may have trouble seeing with only one eye.
Laser-based systems and methods are known for enabling ophthalmic surgery on the cornea in order to correct vision defects by the technique known as ablative photodecomposition. Changing the shape of the anterior surface of the cornea will change the optical properties of an eye. These ablative photodecomposition systems and methods control ultraviolet laser radiation flux density and exposure time upon the cornea so as to achieve a desired surface change in the cornea and thereby correct an optical defect.
Several different ablative photodecomposition techniques have been described to correct specific optical errors of the eye. For example, a myopic condition may be corrected by laser sculpting a corneal surface to reduce curvature. An astigmatic condition, which is typically characterized by a cylindrical component of curvature (departing from the otherwise generally spherical curvature of the cornea), can be corrected by a cylindrical ablation. Laser sculpting a corneal surface to increase the curvature can correct a hyperopic condition.
In a typical laser surgical procedure, the optically functional region of the corneal surface to be ablated is designated the optical zone. Depending on the nature of the desired optical correction, the optical zone may or may not be centered on the center of the pupil or on the apex of the anterior corneal surface. One technique for increasing the curvature of the optical zone for hyperopia error correction involves selectively varying the area of the cornea exposed to the laser beam radiation so as to produce an essentially spherical surface profile of increased curvature. This selective variation of the irradiated area may be accomplished in a variety of ways. For example, the optical zone can be scanned with a laser beam having a relatively small cross-sectional area (compared to the optical zone) in such a manner that the ablation depth increases with distance from the intended center of ablation. The result is a substantially spherical profile for the anterior corneal surface with maximum depth of cut at the extreme outer boundary of the optical zone. Another technique for sculpting the optical zone employs a rotatable mask having a plurality of apertures. The apertures are sequentially introduced into the laser beam path to provide progressive shaping of the laser beam in order to achieve the desired profile.
Efforts have also been made to treat presbyopia using ablative photodecomposition. One specific technique of treating presbyopia creates near-vision correction by ablating a region of the lower portion of the cornea adjacent the pupil rim. With this eccentric positioning of the ablation, the near-vision lens is not centered over the pupil. Consequently, constriction of the pupil may occlude the ablated near-vision lens. Constriction of the pupil is a natural response of the eye to illumination, and could potentially disrupt near-vision.
Alternative suggested presbyopia treatments include laser ablation of a small annular region of the cornea (having a diameter not exceeding 3.5 mm), or the ablation of a central lens for near-vision, surrounded by a gradual blend zone, and then a peripheral far-vision lens, all within the optically used portion of the cornea.
Efforts have been made in the past to laser sculpt a transition zone to provide a more gradual sloping of the walls and to eliminate the sharp discontinuity between the ablation zone and the surrounding untreated cornea. These efforts have included the use of a beam rotation or scanning mechanism operated by a computer to provide programmed ablation of the transition zone to achieve a sigmoid or other profile. While somewhat effective, these efforts often suffer from the added complexity of additional optical elements, such as a rotatable off-axis mirror or revolving prism having suitable optical properties.
2. Description of the Background Art
Systems and methods relevant to laser-based treatments for presbyopia are disclosed in the following U.S. patents and patent applications, the entire disclosures of which are hereby incorporated by reference: U.S. Pat. No. 5,395,356, issued Mar. 7, 1995, for xe2x80x9cCorrection of Presbyopia by Photorefractive Keratectomyxe2x80x9d; U.S. Pat. No. 5,533,997, issued Jul. 9, 1996, xe2x80x9cApparatus and Method for Performing Presbyopia Correctionxe2x80x9d; and U.S. Pat. No. 5,314,422, issued May 24, 1994, for xe2x80x9cEquipment for the Correction of Presbyopia by Remodeling the Corneal Surface by Means of Photoablation.xe2x80x9d
Ablative photodecomposition systems and methods are disclosed in the following U.S. patents and patent applications, the entire disclosures of which are hereby incorporated by reference: U.S. Pat. No. 4,665,913, issued May 19, 1987, for xe2x80x9cMethod for Ophthalmical Surgeryxe2x80x9d; U.S. Pat. No. 4,669,466, issued Jun. 2, 1987, for xe2x80x9cMethod and Apparatus for Analysis and Correction of Abnormal Refractive Errors of the Eyexe2x80x9d; U.S. Pat. No. 4,732,148, issued Mar. 22, 1988, for xe2x80x9cMethod for Performing Ophthalmic Laser Surgeryxe2x80x9d; U.S. Pat. No. 4,770,172, issued Sep. 13, 1988, for xe2x80x9cMethod of Laser Sculpture of the Optically Used Portion of the Corneaxe2x80x9d; U.S. Pat. No. 4,773,414, issued Sep. 27, 1988, for xe2x80x9cMethod of Laser Sculpture of the Optically Used Portion of the Corneaxe2x80x9d; U.S. patent application Ser. No. 07/109,812, filed Oct. 16, 1987, for xe2x80x9cLaser Surgery Method and Apparatusxe2x80x9d; U.S. Pat. No. 5,163,934, issued Nov. 17, 1992, for xe2x80x9cPhotorefractive Keratectomyxe2x80x9d; U.S. Pat. No. 5,556,395, issued Sep. 17, 1996, for xe2x80x9cMethod and System for Laser Treatment of Refractive Error Using an Offset Image of a Rotatable Maskxe2x80x9d; U.S. patent application Ser. No. 08/368,799, filed Jan. 4, 1995, for xe2x80x9cMethod and Apparatus for Temporal and Spatial Beam Integrationxe2x80x9d; U.S. patent application Ser. No. 08/058,599, filed May 7, 1993, for xe2x80x9cMethod and System for Laser Treatment of Refractive Errors Using Offset Imagingxe2x80x9d; U.S. Pat. No. 5,683,379, issued Nov. 4, 1997, for xe2x80x9cApparatus for Modifying the Surface of the Eye Through Large Beam Laser Polishing and Method of Controlling the Apparatusxe2x80x9d; and U.S. Pat. No. 5,827,264, issued Oct. 27, 1998 for xe2x80x9cMethod of Controlling Apparatus for Modifying the Surface of the Eye Through Large Beam Laser Polishing.xe2x80x9d
Techniques for treating presbyopia with contact lenses are disclosed in the following U.S. patents and patent applications, the entire disclosures of which are hereby incorporated by reference: U.S. Pat. No. 5,835,192, issued Nov. 10, 1998, for xe2x80x9cContact Lens and Method of Fitting a Contact Lensxe2x80x9d; U.S. Pat. No. 5,485,228 issued Jan. 16, 1996 for xe2x80x9cMultifocal Ophthalmic Lens Pair;xe2x80x9d and U.S. Pat. No. 5,864,379 issued Jan. 26, 1999 for xe2x80x9cContact Lens and Process for Fitting.xe2x80x9d
It is an object of the invention to mitigate and/or inhibit presbyopia with minimal vision degradation by ablating a transition zone peripheral to an optical zone. It is a further object of the invention to ablate a cornea to produce a healed cornea with an aspheric optical zone that corrects presbyopia. In one aspect, the invention provides for ablating the cornea to a desired shape that compensates for changes in the corneal shape as the cornea heals. In another aspect, the invention provides for the simultaneous correction of presbyopic and other refractive corrections such as nearsightedness, farsightedness and astigmatism. In a yet further aspect, the invention provides for scaling the aspheric optical zone to match the size of the pupil. In yet another aspect, the invention provides for a method for treating presbyopia which includes ablating a transition zone outside an optical zone.
One of the major difficulties encountered in the application of laser surgery techniques to effect hyperopic and presbyopic refractive error corrections lies in the nature of the boundary between the optical zone and the untreated area. When the anterior surface of the cornea is sculpted to have an increased curvature, the maximum depth of cut occurs at the outer boundary of the optical zone. The generally annular region between this outer boundary and the adjacent untreated anterior surface portion of the cornea typically exhibits steep walls after the completion of the photoablation procedure. After the surgery, the eye tends to eliminate these steep walls with a stimulated healing response involving concurrent epithelial cell growth and stromal remodeling by the deposition of collagen, which results in corneal smoothing by filling in tissue in the steep walled region. This natural healing response acts to eliminate the discontinuity, resulting in a buildup of tissue in the steep walled region and over the outer portion of the optical zone. This natural phenomenon, sometimes termed the xe2x80x9chyperopic shiftxe2x80x9d in phototherapeutic keratectomy, causes a lack of precision for a given surgical procedure and diminished predictability, counteracting the beneficial effects of the refractive correction procedure and thereby reducing the desirability of the procedure to the prospective patient.
According to the present invention, the ablated surface can be contoured to provide an aspheric surface on a healed cornea. The invention provides for adjusting the ablation to compensate for factors effecting the final geometry of the healed cornea. These factors include corneal healing and the spatial variation of ablation. The shape of tissue ablated with a uniform laser beam pulse will depend upon the size and shape of the laser beam spot. The spatial variation of the total ablation may also cause variations in the ablated corneal shape. For example, a hyperopic ablation intended to produce a spherical ablation may demonstrate greater steepening near the center of the optical zone. This increased central curvature may form an aspheric surface that corrects for presbyopia.
The ablated surface is covered following the surgery, typically by a new epithelial layer or a repositioned anterior flap of the corneal tissue. Consequently, the final shape of the anterior surface of the cornea may be a different shape than the ablated shape. However, it is the final change in shape of the anterior surface of the cornea, not the initial ablated surface, which determines the refractive change effected by the surgery. Therefore, it may be desirable to ablate a shape on the cornea that is different from the final intended shape on the anterior surface of the cornea. For example, the optical zone may be ablated to a substantially spherical shape for correcting hyperopia. This ablated surface may then heal to an aspheric surface that corrects presbyopia.
The invention includes a method and system for performing ablative photodecomposition of the corneal surface that is capable of providing relatively smooth transition zones along with accurate sculpting of the anterior or other corneal surface to effect simultaneous symmetric or asymmetric refractive and presbyopic corrections with relatively large area coverage. The invention preferably employs a laser beam of smaller beam size than the total treatment area.
The invention further provides for the ablation of an optical zone that substantially matches the area of the pupil. For presbyopic patients, the maximum pupil diameter is typically about 5 mm. Therefore, it is an aspect of the invention that the ablated optical zone have a diameter of about 5 mm, and be user selectable (by the user of the ablation system) to a diameter between 3 and 7 mm. The optical zone is preferably ablated to form a healed aspheric surface. Preferably, the central portion of the optical zone provides near-vision correction and the peripheral portion of the optical zone provides far-vision correction.
The invention additionally provides for scaling a diameter of the aspheric surface to the pupil. This scaling of the aspheric surface permits an appropriate balance between near and far-vision correction within the pupil. For example, a patient with a 5 mm diameter pupil may have a 2.5 mm diameter zone corrected for near-vision, while a patient with a 3 mm diameter pupil may have a 1.5 mm diameter zone corrected for near-vision. Scaling of the aspheric lens may be based on areas of the pupil and/or aspheric surface.
The invention also provides for ablating a transition zone peripheral to the optical zone and to the pupil. This positioning of the ablated transition zone will produce optimal results once the cornea heals. The ablated transition zone provides greater control over the healing process and provides greater control of the shape of the healed surface within the adjacent optical zone. Because the transition zone is ablated to control the shape of an adjacent healed surface, the transition zone may produce a corneal shape which corrects for neither near- nor far-vision. Thus, the transition zone is preferably positioned outside the pupil. Further, the transition zone is preferably sized so that healing of the cornea can be controlled within the adjacent optical zone. The optimal size of the transition zone is an annular region extending radially outward about 2 mm from the outer edge of the ablated optical zone. An ablation with a 5 mm diameter ablated optical zone and an optimally sized ablated transition zone will extend about 9 mm across the cornea. Transition zones of other sizes may be ablated outside the optical zone. Dimensions of the transition zone extending radially outward from the optical zone range from about 1 to 3 mm and preferably from about 1.5 to 2.5 mm.
In a first aspect, the present invention provides a method for reprofiling an anterior surface of the cornea of the eye. The anterior surface is reprofiled from an initial shape to a multifocal aspheric shape for correcting presbyopia. The method comprises aligning a laser system with the eye. The laser system is operable to deliver ablative radiation to the cornea. A surface of the cornea is ablated to a desired shape by selectively exposing the cornea to the ablative radiation. The cornea is ablated to an ablated shape so that an optical zone extends across the pupil and so that a transition zone is disposed beyond the pupil. The ablated surface is covered to produce a final aspheric anterior corneal surface.
In some embodiments, the covering step will comprise regenerating an epithelial layer over an ablated anterior surface of the cornea. In other embodiments, the covering step will comprise repositioning a flap of the cornea over the eye after a portion of either the flap, or the underlying corneal tissues, has been ablated.
In another aspect, the present invention provides an ophthalmic surgery system for performing selective ablation of a corneal surface of the eye so as to create a desired aspheric shape for correcting presbyopia on the anterior surface of a healed cornea. The system comprises means for directing a laser beam along a path. Means are also provided for profiling the beam to produce a profiled beam with a center. Means for displacing the center of the profiled beam over an area of the corneal surface will generally be coupled to the profiling means. A computer controls the positioning of the beam center over the area, and creates a plurality of successive laser beam pulses. The position of the plurality of pulses is determined by a laser treatment table that is scaled to a dimension of a pupil.
In another aspect, the present invention provides a laser eye surgery method comprising selectively ablating corneal tissue from an eye having an uncorrected surface shape. Corneal tissue is ablated so as to produce an initial ablated shape on an anterior surface of the cornea of the eye. The ablated eye heals, and the healed eye has a healed anterior surface shape which differs significantly from the initial ablated shape. This healed shape substantially, and in some instances entirely, corrects a refractive error of the eye.
In yet another aspect, the present invention provides a laser eye surgery method comprising selectively ablating corneal tissue from an eye having a refractive error. The refractive error is selected from the group consisting of myopia, hyperopia, and astigmatism. The ablating step removes a portion of cornea so as to simultaneously correct the refractive error and mitigate presbyopia of the eye.
In yet another aspect, the present invention provides a method for treating presbyopia of an eye. The eye has a pupil, and the method comprises selectively ablating corneal tissue from the eye so as to produce an ablated corneal surface. The corneal surface has an optical zone, and a transition zone surrounding the optical zone. The optical zone of the corneal surface defines an aspheric shape to mitigate the presbyopia, and a dimension of the optical zone substantially matches a dimension of the pupil under scotopic conditions.
In yet another aspect, the present invention provides a method for treating presbyopia of an eye. The eye has a pupil, and the method comprises selectively ablating corneal tissue from the eye so as to produce a corneal surface having an optical zone, and a transition zone surrounding the optical zone. The optical zone of the corneal surface defines an aspheric shape to mitigate the presbyopia. The transition zone is disposed outside of the pupil.
For a fuller understanding of the nature and advantages of the invention, reference should be had to the ensuing detailed description taken in conjunction with the accompanying drawings.